After oil and gas wells are drilled, cased, and cemented it is often necessary to stimulate the reservoir in order for production fluids to flow economically from the well. The fracturing process involves pumping aqueous fluids into the well at a rate sufficient to fracture the rock.
From pumping aqueous liquids at rates sufficient to fracture rock, turbulence develops, creating friction pressure, or drag, resulting in substantial pump energy loss which could otherwise be directed towards fracturing rock. It is thus typical in the fracturing industry to inject materials in small amounts which suppress drag (and thus friction pressure). This is most commonly accomplished in the oilfield via water soluble acrylic polymers and copolymers, added in small amounts to aqueous fracturing fluids. The polymers can be delivered during a fracturing treatment via several means, though most are delivered via oil-external emulsion or from dissolving analogous dry polymers.
The surfactants in these friction reducer emulsions are added to stabilize the polymer as a suspension and often possesses low HLB values (generally between 4 and 8). Upon contact with water, the emulsion “inverts”, resulting in polymer transfer to the water. The inversion is typically facilitated through the use of a subsequent water-soluble “inverting surfactant” of HLB greater than 7. The inverting surfactant may be part of the inverting polymer emulsion, or added to the aqueous solution in which the emulsion is to be inverted.
One problem with known oil-continuous emulsion treatments is that the inverting surfactants may adversely interact with the emulsion and destabilize it. Thus usually inverting surfactants are added to emulsions at less than 5%. Polymer emulsions with this low amount of inverting surfactant may not provide the desired friction reduction because the polymer emulsion either does not invert completely or is not tolerant of concentrated brine nor acidic water found in natural oil well reservoir for example.